1. Field of the Invention
The present invention relates to an optical glass that has a medium to high refractive index and high dispersion characteristics, can be pressed at relative low temperature, and has a relatively low sag temperature and liquidus temperature.
2. Description of Related Art
A number of glasses having medium to high refractive indexes and high dispersion characteristics are known.
For example, Japanese Patent Un-examined Publication No. Hei 07-97234 describes a low melting point optical glass having a medium to high refractive index and high dispersion characteristics and comprising prescribed quantities of P2O5, Na2O, Nb2O5, and WO3. This optical glass is described as having a refractive index of 1.69-1.83, a dispersion ratio of 21-32, and a sag temperature of not more than 570xc2x0 C. However, when comparison is conducted between the examples described in Japanese Patent Un-examined Publication No. Hei 07-97234 having a refractive index of not greater than 1.73, those glasses characterized by having a sag temperature Ts exceeding 520xc2x0 C. are numerous. This is attributed to an Li2O content of 0-0.5 weight percent. Further, there are also examples (Examples 6, 7, and 8) in which Ts is less than 520xc2x0 C. even with an Li2O content within the range of 0-0.5 weight percent. In that case, there is the problem of the use of expensive GeO2 as a glass starting material. When the GeO2 is removed from the glasses of these examples, the liquidus temperature (also referred to hereinafter as xe2x80x9cLTxe2x80x9d) ends up exceeding 900xc2x0 C. This is attributed to a P2O5 content of not greater than 32 percent.
Japanese Patent Un-examined Publication No. Hei 05-270853 describes an optical glass having a medium to high refractive index and high dispersion characteristics and comprising prescribed quantities of SiO2, B2O3, P2O5, Nb2O5, and Na2O+K2O. In the glasses described in this publication, all the glasses described in the examples having a refractive index of 1.64-1.73 have liquidus temperatures exceeding 900xc2x0 C. This is attributed to a P2O5 content of not greater than 32 weight percent. Further, these glasses also have a Ts exceeding 520xc2x0 C. This is attributed to an Na2O content of not greater than 5 weight percent.
Japanese Patent Un-examined Publication No. Sh{overscore (o)} 52-132012 describes an optical glass having a medium to high refractive index and high dispersion characteristics and comprising prescribed quantities of B2O3, P2O5, and Nb2O5. The glasses described in the examples of this publication, which have refractive indexes of 1.64-1.73, all have a Ts exceeding 520xc2x0 C. This is attributed to an Na2O content not exceeding 5 weight percent. Excluding the glasses described in Examples 2 and 3, the lack of Li2O is thought to result in a Ts exceeding 520xc2x0 C. Even in the glasses of Examples 2 and 3 which comprise Li2O in a quantity exceeding 0.5 weight percent, the Ts exceeds 520xc2x0 C. and the liquidus temperature exceeds 900xc2x0 C. This is attributed to a P2O5 content of not more than 32 weight percent and an Nb2O5 content exceeding 30 weight percent.
The press-molding of glass is normally conducted within a high temperature range exceeding the sag temperature temperature Ts of the glass by about 20-60xc2x0 C. When the yield temperature of the glass exceeds 520xc2x0 C., the press temperature becomes at least 540xc2x0 C. Thus, the glass has a strong tendency to react with the molding surface of the mold, shortening the service life of the mold and rendering the glass unsuited to mass production.
When the liquidus temperature is high, the glass tends to lose transparency in the vicinity of its softening point, that is, in the vicinity of the molding temperature in press-molding.
Further, the glass preforms employed in reheating presses are required not to have variation in shape and weight. Thus, when forming preforms by shaping molten glass, the shaping is conducted at a prescribed viscosity where there tends not to be variation in shape and weight. Thus, when the glass is at a temperature at which the viscosity is suited to shaping, it must not tend to lose transparency, that is, the liquidus temperature must be lower than the temperature at which viscosity is suited to shaping. From these perspectives, the liquidus temperature is required to be 800-900xc2x0 C.
However, in the above-described glasses, almost all of those glasses having a refractive index falling within a range of 1.64-1.72 and an Abbxc3xa9 number of 29-36 have a sag temperature temperature exceeding 520xc2x0 C. and a liquidus temperature exceeding 900xc2x0 C. In glasses used in press-molding, when the life of the mold and the tendency of the glass to lose transparency are considered, a sag temperature of not greater than 520xc2x0 C. and a relatively low liquidus temperature, particularly one not greater than 900xc2x0 C., are desirable.
Accordingly, the object of the present invention is to provide an optical glass having a medium to high refractive index and high dispersion characteristics, the liquidus temperature of which is comparatively low, specifically not greater than 900xc2x0 C., and more particularly, an optical glass the refractive index of which falls within the range of 1.64-1.72 and the Abbxc3xa9 number of which falls within the range of 29-36.
The invention relates to an optical glass comprising, by means of weight percentages, more than 32 percent and not more than 45 percent P2O5, more than 0.5 percent and not more than 6 percent Li2O, more than 5 percent and not more than 22 percent Na2O, 6-30 percent Nb2O5, 0.5-10 percent B2O3, 0-35 percent WO3, 0-14 percent K2O, and 10-24 percent Na2O+K2O, and the total of all the above components is not less than 80 percent.
With the above optical glass, the glass preferably comprises, by means of weight percentages, more than 32 percent and not more than 40 percent P2O5, 1-4 percent Li2O, 10-19 percent Na2O, 10-28 percent Nb2O5, 1-5 percent B2O3, 0-8 percent K2O, and 12-22 percent Na2O+K2O, and the total of all the above components is not less than 80 percent. With this optical glass, the glass more preferably comprises 12-17 percent Na2O, 15-26 percent Nb2O5, 0-4 percent K2O, and 14-19 percent Na2O+K2O.
With the above optical glasses, the glass may further comprise, by means of weight percentages, 0-2 percent SiO2, 0-5 percent Al2O3, not less than 0 percent but less than 8 percent TiO2, 0-15 percent ZnO, 0-12 percent BaO, 0-18 percent WO3, not less than 0 percent but less than 1 percent Sb2O3, and 0-1 percent SnO2, and the total of all of the above components and the components listed in any one of claims 1 to 3 is not less than 95 percent. With this optical glass, the glass preferably comprises, by means of weight percentages, 0-3 percent Al2O3, 0-6 percent TiO2, and 0-9 percent ZnO, where the total of all of the components listed is not less than 95 weight percent; and the glass preferably comprises 0-1 percent SiO2.
With the above optical glasses, the glass may comprise not less than 0 percent but less than 0.5 percent SiO2, 0-5 percent TiO2, 0-5 percent ZnO, and the total of all of the components listed is not less than 98 percent; and the glass may further comprise 3-15 weight percent WO3.
The invention further relates to an optical glass comprised phosphate glass which comprises, by means of weight percentages, more than 0.5 percent and but not more than 6 percent Li2O, more than 5 percent but not more than 22 percent Na2O, 0-14 percent K2O, 10-24 percent Na2O+K2O, 6-30 percent Nb2O5, and not more than 45 percent P2O5, and exhibits a refractive index (nd) of 1.64-1.72, an Abbxc3xa9 number (vd) of 29-36, and a sag temperature (Ts) of not greater than 520xc2x0 C.; and an optical glass comprised of phosphate glass which comprises, by means of weight percentages, more than 0.5 percent but not more than 6 percent Li2O, more than 5 percent but not more than 22 percent Na2O, 0-14 percent K2O, 10-24 percent Na2O+K2O, 6-30 percent Nb2O5, 0-35 percent WO3, 0-5 percent Al2O3, and not less than 0 percent but less than 8 percent TiO2, and exhibits a refractive index (nd) of 1.64-1.72, an Abbxc3xa9 number (vd) of 29-36, and an sag temperature (Ts) of not greater than 520xc2x0 C.
With these glasses, the glass preferably comprises more than 32 weight percent but not more than 45 weight percent P2O5.
The invention still further relates to an optical glass comprising, by means of weight percentages, more than 32 percent but not more than 45 percent P2O5, more than 0.5 percent but not more than 6 percent Li2O, more than 5 percent but not more than 22 percent Na2O, 6-30 percent Nb2O5, 0.5-10 percent B2O3, 0-35 percent WO3, 0-14 percent K2O, 10-24 percent Na2O+K2O, 0-2 percent SiO2, 0-5 percent Al2O3, not less than 0 percent but less than 8 percent TiO2, 0-15 percent ZnO, 0-12 percent BaO, not less than 0 percent but less than 1 percent Sb2O3, and 0-1 percent SnO2, where the total of the contents of each of the above-listed components is not less than 95 percent, the refractive index (nd) is 1.64-1.72, the Abbxc3xa9 number (vd) is 29-36, and the sag temperature (Ts) is not more than 520xc2x0 C.
The invention further relates to an optical glass comprised of phosphate glass which comprises Li2O, Na2O, Nb2O5, and B2O3 as essential components, and not more than 2 weight percent SiO2 an optional component, with a refractive index (nd) of 1.64-1.72, an Abbxc3xa9 number (vd) of 29-36, a sag temperature (Ts) of not more than 520xc2x0 C., and a liquidus temperature (LT) of not more than 900xc2x0 C.
With this optical glass, the glass may further comprise, by means of weight percentages, more than 32 percent but not more than 45 percent P2O5, more than 0.5 percent but not more than 6 percent Li2O, more than 5 percent but not more than 22 percent Na2O, 6-30 percent Nb2O5, and 0.5-10 percent B2O3.
With all of the optical glasses mentioned above, the glass may further comprises, by means of weight percentages, 0-5 percent MgO, 0-5 percent CaO, 0-5 percent SrO, 0-3 percent La2O3, 0-3 percent Y2O3, 0-3 percent Gd2O3, 0-3 percent ZrO2, not less than 0 percent but less than 1 percent AS2O3, 0-3 percent Ta2O5, 0-3 percent In2O3, 0-3 percent TeO2, 0-3 percent Bi2O3, and 0-1 percent GeO2, where the total of the above-listed components and the components described in any one of claims 1 to 14 is not less than 99 percent.
The invention still further relates to an optical article comprised of the optical glass according to the present invention; an optical glass for precision press-molding wherein the glass is one according to the present invention; a glass preform obtained by preforming the above optical glass; a glass optical article obtained by reheat press-molding the above glass preform; and an optical article obtained by press-molding the optical glass according to the present invention.